Baby Center's Due Date Calculator uses the same approach that your provider is likely to use.
It gives you a due date that's 40 weeks from the first day of your last period.
This time -- 14 days after your period started and a day or so longer -- is when you're the most fertile.
If you want to get pregnant, this is the best time to try.
Another study in 2013 found that even where the date of ovulation was known, the length of pregnancy varied by 37 days — even if they excluded women who had complications or preterm births.
So when you try Belly Belly's due date calculator (with adjustable cycle lengths), you will be able discover an approximate date when your baby will arrive, but keep fluctuations in mind.
Pregnant and wondering when your baby might be due?
Belly Belly's due date calculator will give you an estimated date of birth to mark on your calendar.
The likelihood of actually becoming pregnant is dramatically increased if you have intercourse in the three days leading up to and including ovulation. Depending on your cycle length the most fertile days in the cycle varies: Women’s cycles can vary and are not always as regular as clockwork, so to know that you are ovulating and on which day of your cycle you are ovulating, observe your fertility signs throughout your cycle and record them on a chart.
Human gestation is the same for everyone: It takes about 38 weeks from the day of conception to the day you deliver.
If you do happen to know precisely when you conceived – perhaps you were tracking your ovulation and you know on which day your egg must have been fertilized – we give you the option of calculating your due date based on your conception date. Your healthcare provider might revise your due date if she has reason to believe it's off target.